Currently, there exist only a couple of pieces of basic exercise equipment that allow for rotational plane exercises. The most popular being a medicine ball with a rope attached to it. The premise of this system is that the individual holds onto the rope with their hands and swings the ball in whatever rotational plane they desire. When the rotational plane is reversed, a plyometric contraction takes place as the body employs antagonistic muscles to reverse the rotational forces.
The device can also be used in a manner that allows the ball to strike a solid body like the ground or a solid wall. This action allows for the rapid deceleration of the weight and assists the individual in changing the direction of rotation without having to retard the velocity using muscular force. This allows for the individual to rapidly disengage the agonist muscles and engage the antagonist muscles without the need to slowly decelerate the movement first with muscle resistance.
Although this system is an effective way of developing core muscles and creating explosive muscle contractions, it is limited in the following ways. First, the rope is a singular extension from the medicine ball which allows the rope to be held only in a manner similar to holding a baseball bat. This causes the forces that act on the rope to pivot at the top of the griping hand closest to the medicine ball. Since the rope is flexible and incapable of transferring the forces further past the pivot point of the closest hand, the further hand offers no assistance in inducing or retarding any forces created once the medicine ball is put in motion. This creates an asymmetrical action, where only one arm is truly being exercised. This in turn causes the core to be utilized in an asymmetrical fashion that could potentially lead to over use injuries.
Second, the rope is directly tied to the medicine ball. This causes binding of the rope as the ball spins around its own axis of rotation. This binding causes torque forces to travel the rope. This torque force can work against the grip of the user and can dramatically limit the life of the product.
Third, the functionality of the system is limited to dynamic rotational exercises. The only exercises that can be conducted statically involve suspending the ball from the rope and using muscle force to fight gravity in the opposite direction. This means that the system only allows for resistance directly upwards from the ground. Add to this that only one arm truly assists in this movement and the static exercises are extremely limited.
Fourth, the rope system causes extreme friction to the hands of the user causing extreme discomfort from both friction and the binding forces from the leverage point created at the end of the grip. This is typically compounded by the fact that users will wrap the rope around their hand to give extra gripping ability. This causes the rope to exert an enormous squeezing force across the metacarpals that could lead to serious injury.
Finally, this system utilizes a fixed weight. The rope is permanently affixed to the medicine ball. This means that anyone wanting to utilize a larger or smaller weight must purchase an entirely separate unit.
U.S. Pat. No. 7,044,896 by Hetrick discloses one example of an exercise device using two inelastic straps connected to respective hand grips in which the straps are commonly anchored to a suitable anchor which is secured to a stationary object. The user can thus perform various exercises but is generally limited to exercises working against the stationary object or using their own body weight as resistance.